Endoluminal prostheses may be inserted into a body lumen such as an anatomical vessel or duct for various purposes. Prostheses may maintain or restore patency in a formerly blocked or constricted passageway, for example, following a balloon angioplasty procedure. Other prostheses may be used for different procedures. For example, a prosthesis may include one or more stents placed in or about a graft, and the stents may hold the graft in an open configuration to treat an aneurysm. Additionally, stents coupled to one or both ends of a graft may extend proximally or distally away from the graft to engage a healthy portion of a vessel wall away from a diseased portion of an aneurysm to provide endovascular graft fixation.
Stents may be either self-expanding or balloon-expandable. In some examples, stents can have characteristics of both self-expanding and balloon-expandable stents. Self-expanding stents may be delivered to a target site in a compressed configuration and subsequently expanded by removing a delivery sheath, removing trigger wires, and/or releasing diameter reducing ties. A self-expanding stent expands primarily based on its own expansive force without the need for further mechanical expansion. A stent may be made of a shape-memory alloy such as nitinol. The shape-memory alloy may be employed to cause the stent to return to a predetermined configuration upon removal of the sheath or other device maintaining the stent in its predeployment configuration.
Deployment devices are used to deploy prostheses, particularly those including self-expanding stents, within various body lumens. In some deployment devices, trigger wires are used to restrain a prosthesis in a particular position on the deployment device or to restrain one or more self-expanding stents of the prosthesis in a compressed state. The trigger wires may releasably couple the proximal and/or distal ends of the prosthesis to the deployment device. Typically, one or more trigger wires are looped through a portion of a stent near a vertex of the stent. For example, trigger wires may be used to restrain a “Z-stent” or Gianturco stent having a series of substantially straight segments interconnected by a series of bent segments. The trigger wires may be disposed through, and pull upon, the bent segments to pull the stent closely against the deployment device.
In the region of the deployment device in which the prosthesis is carried, trigger wires can foul or catch with stent components on the prosthesis, particularly when the deployment device is bent to pass through convolutions in the anatomical vessel or duct. This may cause inaccurate deployment or even jamming or breakage of the trigger wire.
Trigger wires also may be used in conjunction with different stent designs such as cannula-cut stents having relatively acute or pointed bends. The designs of cannula-cut stents may facilitate compression of the stents to a relatively small delivery profile due to the tight bends of the apices. With such stents, the trigger wires may be looped around one or more vertices formed at the proximal and/or distal apices, e.g., a location where an individual apex splits into two separate strut segments.
If trigger wires are threaded through the vertices of such cannula-cut stents, the trigger wires may become crimped at the vertices during compression of the stents to a reduced diameter delivery profile. If the trigger wires are crimped between the strut segments, the trigger wires and/or strut segments may become damaged. Furthermore, when compressing cannula-cut stents having relatively acute bends to a significantly reduced radial profile, barbs disposed near the apices of the stents may become entangled with the stent struts and/or the trigger wires.
Typically, multiple trigger wires are threaded through multiple vertices of a stent to restrain the end of the stent in the reduced diameter delivery profile. Additional trigger wires may be added to more securely restrain the stent. However, such additional trigger wires may increase the retraction force that is required to release the stent. Such additional trigger wires also may increase the likelihood of one or more of the trigger wires becoming entangled with portions of the stent such as barbs.
In view of the above, it would be desirable to provide an apparatus configured to release a stent with a reduced retraction force while also reducing the likelihood of entanglement and damage to the trigger wires and stent struts.